In the semiconductor fabrication process, a square cross-sectional or rectangular cross-sectional container made of a plastic material is frequently used to transport articles. These articles may include silicon wafers, reticles or other substrates used for building IC devices. A reticle is a transparent ceramic substrate that is coated with a metallic layer forming a pattern for an electronic circuit. It is generally used in an imaging step during a photolithographic process wherein a pattern of a circuit is reproduced on the surface of an electronic substrate, i.e., on a wafer surface.
A reticle can be constructed of any suitable transparent ceramic materials. One of the most commonly used material is quartz or silicon dioxide. A quartz reticle can be readily coated with a chrome layer at selective areas to reproduce an electrical circuit. The chrome metal layer may be formed by either a pure chromium or a chromium alloy. During a photolithographic imaging process, a light source is projected from one side of the reticle that is coated with the pattern such that the pattern can be reproduced on the surface of a wafer which is positioned on the opposite side of the reticle. The pattern for the electronic circuit coated on the reticle is frequently laid out in a 5.times. magnification. The true dimensions of the electronic circuit reproduced on the wafer surface can be obtained by suitably adjusting the optical lenses situated between the reticle and the wafer. Metallic coatings other than chrome may also be coated on the surface of the reticle for the circuit lay-out. However, chrome has been found to be an ideal material for its appearance of a brownish tone and its ease of identification by human eyes.
In a semiconductor fabrication facility, static electricity or electrostatic discharge frequently develops on surfaces of articles made of insulating materials when they are touched or rubbed by other insulating materials such as insulating gloves. The electricity is produced based on a triboelectricity theory. The discharge of the static electricity to machines and to human operators can cause damages to semiconductor wafers and process tools. Sometimes, it may even cause injury to a machine operator. In a semiconductor fabrication facility, it is therefore necessary to control ESD by grounding the machines, by controlling the relative humidity, or by building walls and floor coverings with slightly conductive materials such that electrical charges can be routed to ground. When the triboelectricity is suitably controlled, the control of dust and particulate contamination is also enhanced. For instance, the metal racks, pipe lines, cabinets, cables and rails are normally grounded in a facility to an equal potential bar or to a planar ground. The metal pedestals of the raised floor are then connected to the planar ground under the raised floor. To further enhance ESD protection, the metal framework of the clean room wall systems are also connected to the planar ground. Air ionization systems are frequently installed at selected locations in a fabrication facility, to provide additional ESD control.
Despite the elaborate efforts spent in grounding process machines and various facilities, ESD damages still occur in a fabrication facility. A typical example is the occurrence of ESD when an insulating material is shipped or transported in a container made of another insulating material. For instance, when a reticle is transported from a storage facility to a photolithography machine in a container, i.e., a pod, that is normally constructed of a thermoplastic material. Since the reticle itself is an insulating material, i.e., a quartz or other silicon dioxide materials coated with a chrome coating, when the pod is handled by machine operators wearing insulating gloves, the static charge on the pod drastically increases due to friction generated between two insulating articles. Since the pod is not equipped with an anti-electrostatic device, high static electricity cumulates on the surface of the pod. For instance, it has been confirmed that the static electrical field generated on a pod surface increases from 0.1 KV/inch to nearly 15 KV/inch when a polycarbonate pod is rubbed with PVC gloves. Such a high static electricity build-up on the surface of the pod immediately causes an electrostatic discharge between the pod and the reticle contained therein. When ESD occurs between the pod and the reticle, the pattern on the reticle surface is usually damaged to such an extent that it can no longer be used for imaging. Conventional air ionization devices installed at a fabrication facility are not useful for preventing such ESD damages.
Others have proposed techniques for controlling or minimizing ESD damages to reticles carried in plastic containers. For instance, anti-electrostatic-type plastic materials, such as Bayon.RTM. has been used for the construction of the pod. However, due to its high cost, this type of anti-electrostatic plastic material cannot be widely utilized in a fabrication facility. Still others have proposed the use of gloves that are made of a conductive material such as Propex.RTM. so that the generation of electrostatic discharge can be avoided. The high cost of the Propex.RTM. gloves prohibits its broad usage in the processing industry.
Referring initially to FIG. 1 where it is shown a cross-sectional view of a container equipped with a conventional reticle support system. The container 10 is constructed of a top lid 12, a bottom lid 14, a left sidewall 18 and a right sidewall 16. The front and rear sidewalls (not shown) are constructed of similar materials, i.e., a thermoplastic material such as polycarbonate or polymethylmethacrylate. Support means 22 are positioned on the bottom lid 14 of the container for supporting a reticle 24. The reticle 24 is normally constructed of a transparent ceramic material such as quartz or other types of silicon dioxide. On a surface 26 of the reticle 24, a pattern 28 is formed by coating the surface with a suitable metallic material. The pattern 28 can be formed by one of many suitable metallic materials. A handle 32 is affixed to the top lid 12 of the container 10 for easy carrying by an operator. The d.sub.2 value for the commercially obtained container is 3.365 cm.
In the conventional reticle container shown in FIG. 1, electrostatic discharge (ESD) damage is frequently encountered during a reticle handling process. Electrostatic charges may cumulate on the reticle pod, which in turn induce mask chrome feature damage by an electrostatic discharge. A damaged reticle may result in thousands of defective circuits being produced. With the recent advent in deep submicron technology, the ESD phenomenon becomes more serious as chrome feature on the reticle becomes smaller and closer together. An ESD easily occurs even at a lower electrical potential resulting in the chrome pattern melting and bridging. In most integrated circuit fabrication facilities where ESD problems are encountered, various approaches in eliminating the problem have been attempted regarding the issues of handling, equipment grounding, use of ionizer equipment and use of conductive materials for forming reticle storage boxes. However, most of these approaches are either too costly or cannot be used to retrofit thousands of reticle storage boxes already in use in the fab facility.
It is therefore an object of the present invention to provide an electrostatic discharge-free container that is equipped with a metal shield for holding an insulating article that does not have the drawbacks or shortcomings of the conventional containers that are made of an electrically insulating material.
It is another object of the present invention to provide an electrostatic discharge-free container that is equipped with a metal shield on the bottom lid of the container to substantially cover the bottom lid.
It is a further object of the present invention to provide an electrostatic discharge-free container that is equipped with a metal shield in a cup-shape to substantially surround an insulating article positioned in the container.
It is another further object of the present invention to provide an electrostatic discharge-free container that is equipped with a metal shield formed of a metal layer covering a bottom lid of the container and a cup-shaped metal enclosure which substantially surrounds the insulating article carried in the container.
It is still another object of the present invention to provide an electrostatic discharge-free container that is equipped with a metal shield wherein the metal shield is fabricated of a contaminant particle-free metallic material.
It is yet another object of the present invention to provide an electrostatic discharge-free container that is equipped with a metal shield inside the container and a metal knob in the top lid of the container.
It is still another further object of the present invention to provide an electrostatic discharge-free container that is equipped with a metal shield inside the container fabricated of stainless steel.
It is yet another further object of the present invention to provide an electrostatic discharge-free container that is equipped with a metal shield which includes a metal layer encapsulated inside a bottom lid as an insert that overlap substantially the bottom lid.